Professor Ansarian said: Monotheism is the foundation of religion, being and existence; and it has neither beginning nor end, Allah has placed this principles in the term of «لا اله الا الله», "there is no Allah except Allah" That is, the Lord does what nobody does until the Day of Resurrection, and it is strange that the Lord of the universe combines this word and promises a reward for it, in a way that astonishes everyone.
Give this "there is no Allah except Allah" to Allah and he gives the paradise to you in return.
Professor Ansarian talked about the term "there is no Allah except Allah" and said: Prophet (PBUH) says: this precious word which is granted to you by Almighty Allah can be used to buy paradise with. The Allah Almighty has given you the price of paradise because you cannot purchase it on your own. The lord of the universe has given you this due to his extensive mercy, he has asked you to say "there is no Allah except Allah" and I will give the paradise.
source : erfan.ir